The present invention relates to an electron gun for a cathode ray tube. More specifically, the present invention relates to a technique to improve a high frequency magnetic field transmission property of an electron gun.
FIG. 6 shows a structure of a conventional electron gun for a projection-type monochrome cathode ray tube disclosed in JP-A-10-74465. FIG. 6 is an enlarged cross-sectional view of a neck tube portion.
As shown in FIG. 6, the state-of-the-art for improving focusing performance is subjecting the electron gun disposed inside a neck tube 3 to magnetic field modulation caused by a velocity modulation coil 20 from outside of the neck tube 3 in order to carry out velocity modulation of an electron beam. Namely, an electron beam (not shown) emitted from a cathode 7 housed in a G1 electrode (control electrode) 6 is modulated by an alternating magnetic field generated by the velocity modulation coil 20, a convergence yoke 23, a deflection yoke 24 and the like, during a passage of the electron beam from a G2 electrode (acceleration electrode) 8 to a phosphor screen surface (not shown).
The deflection yoke 24, which is attached to a funnel cone portion of the cathode ray tube, generates an alternating magnetic field to deflect an electron beam, so that the electron beam scans the phosphor screen surface of the cathode ray tube. The convergence yoke 23, attached to the outside of the neck tube 3 of the cathode ray tube, corrects raster distortion and color displacement by generating an alternating magnetic field 22 to modulate the electron beam. The velocity modulation coil 20 is attached to the outside of the neck tube 3 of the cathode ray tube and generates alternating magnetic field 21 to modulate the scanning speed of the electron beam in order to prevent a high-intensity part on the phosphor screen from extending to a low-intensity part and to sharpen images.
The frequency of an alternating magnetic field for modulating an electron beam ranges from a deflection frequency (15.75 kHz) to a mega-Hertz order equivalent to a frequency for images. Therefore, when an electron gun includes metal portions formed by deep-drawing metal materials such as stainless steel, the alternating magnetic field is damped and a desired electrode beam modulation cannot be obtained.
As shown in FIG. 6, the deflection yoke 24 is attached to the funnel cone portion. A portion of an alternating magnetic field 19 generated by the deflection yoke 24 passes a second anode 11 (G5 electrode). A portion of the alternating magnetic field 22 generated by the convergence yoke 23 passes the second anode 11. The velocity modulation coil 20 is disposed between a first anode 9 (G3 electrode) and a focusing electrode 10 (G4 electrode). A portion of the alternating magnetic field 21 generated by the velocity modulation coil 20 passes the first anode 9 and the focusing electrode 10. When an alternating magnetic field is applied through these metal electrodes, an eddy current is generated at the metal electrodes. The eddy current loss is increased as the frequency of the alternating magnetic field becomes high. Thus, the modulation effect of the electron beam due to the magnetic field in the high frequency modulation band is reduced.
It is an object of one or more embodiments of this invention to solve these problems and provide an electron gun for a cathode ray tube, which can provide a desired electron beam modulation effect substantially without interrupting transmission of the modulation magnetic field from the exterior.
An electron gun for a cathode ray tube according to the present invention includes a plurality of arranged tubular electrodes for passing electron beams inside the electrodes, the tubular electrodes being fixed to support rods respectively by support members. At least one of the tubular electrodes is separated into two parts, and the separated tubular electrode parts are connected electrically with each other by a coil member provided between the tubular electrode parts. Each coil member is composed of a wire with its tip ends being located within spaces formed by the support members.
Accordingly, an eddy current loss can be lowered since a modulation magnetic field passes through clearances between wire parts composing the coil member. Further, electric field emission of electrons from tip ends of the coil members is suppressed due to the location of the tip ends.
Preferably, each support member has a U-shape when viewed in the axial cross section, and each tip end of the wire composing the coil member is located within the space formed by a pair of parallel plates composing the support member. Thereby, a tip end of the coil member is located within a space formed by the support member and the support rod in order to reduce the exposed areas, and thus, electric field emission from the tip ends can be decreased.
It is preferable that the tip end of the wire is located at the central portion of the space in the axial direction. This configuration improves the effects for decreasing the electric field emission.
It is preferable that the coil member before being assembled into an electron gun has an inner diameter that is substantially the same as or smaller than an outer diameter of the separated tubular electrodes. The end portions of the separated tubular electrodes are inserted into the coil member, so that the tubular electrodes and the coil member are fitted and fixed to each other. Accordingly, the tubular electrode and the coil member can be fixed without welding.
Also it is preferable that the coil member before being assembled in the electron gun is longer than a mutual spacing between the respective support members of the separated tubular electrodes. The coil member presses the support members with the spring force so that the coil member is fixed to the tubular electrodes. Thus, the tubular electrode parts and the coil member can be fixed without welding.
Another electron gun according to the present invention comprises a plurality of arranged tubular electrodes for passing electron beams inside thereof, the tubular electrodes being fixed to support rods respectively by support members. At least one of the tubular electrodes is separated into two parts, and the two separated tubular electrode parts are connected electrically with each other by a coil member provided therebetween. Each coil member before being assembled into an electron gun has an inner diameter that is substantially the same as or smaller than an outer diameter of the separated tubular electrode parts. The end portions of the separated tubular electrodes are inserted into the coil member, so that the tubular electrodes and the coil member are fitted and fixed to each other.
Accordingly, the tubular electrode and the coil member can be fixed without welding.
It is preferable that the coil member before being assembled in an electron gun is longer than a mutual spacing between the respective support members of the separated tubular electrode parts. The coil member presses the support members with its spring force so that the coil member is fixed to the tubular electrode parts.
Thereby, the tubular electrode and the coil member can be fixed without welding.